Steerable vehicle

ABSTRACT

A steerable, self-propelled vehicle includes a rotatable steering column that is connected to control the steering angle of one or more ground-engaging members of the vehicle. The vehicle includes between the steering column and the ground-engaging member a first steering servomechanism having at least a first steering assistance characteristic; a second steering servomechanism having a second steering assistance characteristic also being connected to act on the steering column. A controller is provided for causing the first and second steering assistance characteristics to influence the steering of the vehicle in dependence on one or more one or more control commands generated in the controller.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. application Ser. No. 15/266,077, entitled “A STEERABLE VEHICLE”, filed Sep. 15, 2016, which is a continuation of U.S. application Ser. No. 14/342,956, entitled “A STEERABLE VEHICLE,” filed Jul. 11, 2014, now U.S. Pat. No. 9,469,340, which is a U.S. National Stage filing of International Application Serial No. PCT/EP2012/067082, entitled “A STEERABLE VEHICLE,” filed Sep. 3, 2012, which claims priority to Italian Application Serial No. TO2011A000795, filed Sep. 7, 2011. Each of the forgoing applications is hereby incorporated by reference in its entirety.

FIELD

This disclosure relates to a steerable, preferably driver-operated, self-propelled vehicle. In particular the disclosure relates to a relatively heavy vehicle that is required to perform differing maneuvers on a variety of types of surface. The disclosure therefore is applicable e.g. to construction vehicles such as excavators, bulldozers and backhoe loaders; certain classes of military vehicle; and agricultural vehicles such as tractors, in respect of which the present disclosure is most strongly applicable; farm loaders/grabs; and multipurpose vehicles (i.e. a pick-up-type vehicle having a forward cab, a pick-up deck, a four wheel drive powertrain equipped with off-road tires and a low ratio transfer box permitting the towing of agricultural implements).

BACKGROUND

It is well known to provide power assistance to the steering sub-systems of driver-operated vehicles.

In various types of vehicle it has for many years been commonplace, especially in the case of relatively large vehicles in which the required steering effort may be significant, to provide power assistance in the form of a hydraulic servomechanism. This includes a pump for pressurizing a fluid such as hydraulic oil in a circuit that includes a servo valve. The degree of opening of the servo valve is determined by turning of the steering column, of the vehicle, that is coupled to an input shaft of the valve by way of a mechanical linkage.

The valve pilots the hydraulic fluid pressure, in dependence on the resulting valve setting, to an assist motor that in some applications is a linear hydraulic cylinder having at each end an extensible arm and in some other applications may be e.g. a hydrostatic motor.

The cylinder when fitted interconnects by way of the ends of the arms the steerable wheels of the vehicle in replacement of conventional, solid steering linkage members. The cylinder may act in the same manner as the rigid linkages or, when extension of the arms occurs as a result of operation of the servomechanism, to reduce the effort needed to turn the steering wheel against the resistance provided by the mass of the vehicle acting through the steerable wheels.

Power assistance of this general kind renders the feeling of the steering “light” (i.e. relatively effortless) as experienced by the driver of a vehicle equipped with it. Moreover if the servomechanism fails for any reason the cylinder becomes rigid and behaves in the same manner as a conventional linkage member. In consequence it remains possible to steer the vehicle, albeit through the application of considerably more effort on the part of the driver, in the event of a servomechanism fault developing.

One characteristic of hydraulic servomechanisms of the general kind described above however is that they do not on their own provide a “self-centering” characteristic. This is of course important in most self-propelled, driver-controlled vehicles since it is strongly desirable that the steerable wheels return to a “straight ahead” setting in the event of the driver releasing a steering input member (that in a passenger car and the majority of the vehicle types listed is a steering wheel).

Passenger vehicle steering is normally designed to incorporate a positive caster angle that gives rise to a mechanical self-centering effect. This tends to provide directional stability when the vehicle is driven on relatively smooth, metalled roads as is normally the case for such a vehicle.

A self-centering steering effect is of limited benefit in the case of agricultural vehicles when they are operating in off-road situations such as when driving in fields.

This is partly because furrows or other features of e.g. a ploughed field tend to override any self-centering effect brought about through design features including positive camber angles. The forces induced by the furrows on the steerable wheels (or other ground-engaging members of the tractor, if fitted) exceed any self-centering forces induced by the steering geometry.

Moreover under many circumstances when operating in a field a tractor operator may find a self-centering effect to be inconvenient. Examples arise when turning at a headland, or when following a curved margin of a field, when driving on lateral slopes (in a so-called “crab-like motion”), or when ploughing with two wheels in a furrow.

At such times it may be desirable in effect to “set” a steering angle for an extended period of operation. The tractor driver therefore may find it bothersome to have to adjust the steering input member continuously in order to overcome a self-centering effect and assure constancy of the steering angle.

In any event a modern tractor is a complicated multi-purpose vehicle that may be fitted with or coupled to numerous sub-systems (such as harvesters, spraying equipment and tilling implements) that require operation from within the operator's cab. When operating such sub-systems the driver may find it very difficult simultaneously to make steering input adjustments.

On the other hand when moving in a straight line on a relatively flat field, or when driving on roads, a tractor operator may find it desirable for the tractor to behave in ways that are similar to other road vehicles, and thereby exhibit a self-centering steering effect or other effects that are useful from the standpoints of safety, stability and/or convenience.

Another known type of power steering assistance mechanism is an electric type, in which rotations of the steering column are converted (e.g. using a Hall effect device, or another kind of sensor) into electrical signals. These in turn may be used to generate commands for an electric motor that is connected to provide rotational assistance forces to the steering column. Indeed in some arrangements the shaft of the steering column itself is constituted over part of its length as the rotor of the motor.

It would be desirable to be able to adjust the characteristics of the steering of a large, heavy vehicle that operates under varying circumstances, to take account of the prevailing type of use. The presence or absence of a self-centering steering effect is exemplary of the kind of characteristic it could be desirable to adjust, although there exist others such as but not limited to the degree of damping of the steering (i.e. the extent to which the steering deviates from a set steering angle); the extent to which power assistance applies to assist the vehicle operator; assistance in turning from one lock to the opposite lock as quickly as possible; and more general transitions of characteristics that take account of changes from rough off-road to on-road or smooth field driving.

SUMMARY

The present disclosure discloses one or more advantages not available in existing power steering assistance. To this end according to the disclosure in a broad aspect there is provided a steerable, self-propelled vehicle including a steering mechanism having a rotatable steering column that is connected to control the steering angle of one or more ground-engaging members of the vehicle, the vehicle including acting on the steering mechanism at a first location (e.g. at an end of the steering column and lying between the steering column and the ground-engaging member) a first steering servomechanism having at least a first steering assistance characteristic; acting on the steering mechanism at a second location, e.g. part-way along its length a second steering servomechanism having a second steering assistance characteristic; and a controller for causing the first and second steering assistance characteristics to influence the steering of the vehicle in dependence on one or more driver inputs and/or one or more control commands generated in the controller.

The presence of two servomechanisms having differing assistance characteristics, together with a controller for determining the extent to which each of them confers its assistance characteristic(s) on the steering of the vehicle, means that it is possible to provide a wide variety of steering modes in the vehicle. These may be designed for example for when travelling in a ploughed field or on rutted ground, or for when travelling on smoother surfaces. A variety of other characteristic choice criteria may equally well form the basis for a design/control philosophy based on the disclosure as broadly stated.

By “connected” herein is meant a variety of ways of causing or permitting one component or sub-system to influence another. Thus for example the steering column may be connected to control the steering angle of the one or more ground-engaging members by way of a physical (mechanical) connection or an electronic connection involving servomotors and signal wires or wireless communication protocols. Another possibility is for the connection to be by way of fluid power components such as hydraulic or pneumatic circuits.

In certain embodiments, the vehicle is driver-operated, but as explained below this need not necessarily be the case.

Preferably the first steering servomechanism is a hydraulic steering servomechanism including a hydraulic steering valve that generates a pilot hydraulic signal in relation to the rotational angle of the steering column and at least one hydraulic steering cylinder connected to adjust the steering angle of the one or more ground-engaging members, the pilot hydraulic signal being piloted to control the hydraulic steering cylinder.

The first steering servomechanism therefore may in certain embodiments be similar to known hydraulic power steering systems of the kind described above. Indeed it is possible within the scope of the disclosure to adapt known power steering hydraulic systems at low cost for use as the first servomechanism. In other embodiments, however, the first servomechanism may be of other designs.

Also preferably the second steering servomechanism is an electric power steering servomechanism including a motor for generating a torque (rotational force) that acts on the steering column; and a signal generator for generating control signals determining the magnitude and direction of action of the torque.

The use of an electric power steering servomechanism means that it is readily possible to provide, in the vehicle, a hybrid steering assistance arrangement in which the two servomechanisms have differing, yet readily combined, characteristics.

In like manner to the first servomechanism the second servomechanism may be of the kind described above, or may of another type as desired and depending on the precise application under consideration.

Conveniently the controller is programmable and the vehicle includes a human-machine interface (HMI) using which a driver may input commands selecting two or more programmed modes of operation of the steering servomechanism.

The HMI may be designed to provide for ease, and speed, of use, thereby minimizing the extent to which a tractor driver must pay attention to the selection of steering assistance modes while performing difficult maneuvers. To this end when the vehicle is an agricultural vehicle the HMI includes switching interfaces for selecting between programmed modes that control steering during movement of the tractor respectively in a field headland and in other locations.

Preferably the HMI includes respective switches for selecting the programmed modes and sequentially selecting sub-modes following selection of a said programmed mode. Thus, in certain embodiments, the HMI may permit “scrolling” through a sequence of selectable modes in a manner that is extremely simple to achieve and that can be completed quickly.

Optionally and preferably the other locations include but are not limited to fields and roads.

In certain embodiments, the sub-modes available following selection of headland operation include a damped steering sub-mode, a maximal assistance (“effortless”) sub-mode, automatic steering centering sub-mode and a lock-to-lock assistance sub-mode as defined herein; and the sub-modes available following selection of other location operation include an on-road sub-mode, a damped steering sub-mode and a maximal assistance (“effortless”) sub-mode as defined herein.

Conveniently the vehicle includes two or more selectively operable steering input members connected to the steering mechanism that are or include a steering wheel and a joystick. The steering system, therefore, is suitable for use in an agricultural tractor or backhoe loader in which a joystick control is provided for the purpose of permitting a driver to steer the tractor when his seat is reversed and he/she is viewing operations of the vehicle via a rearwardly facing window of the operator cabin.

When present the steering wheel preferably is mechanically coupled to the steering column, although it is possible for the steering wheel to be an electronic input device that generates electrical signals instead of being directly physically coupled to the steering column. The joystick preferably is electronically coupled to the second steering servomechanism, although in certain embodiments it may be connected by way of a pneumatic or hydraulic movement mimic circuit, or even a mechanical linkage.

Although conventionally the phrase “steering column” refers to an elongate, shaft-like column that is rigid in normal use and extends from the forward bulkhead of the vehicle cab to connect to forwardly mounted steering linkage components, this need not necessarily be so. Thus, the steering system of the vehicle may operate principally on the basis of electronic commands (a so-called “steer-by-wire” arrangement) and the steering column may in that case need to be long enough only to journal a steering wheel relative to the cab fascia or dashboard. The first and second servomechanisms may be manufactured in such sizes and may be located on the steering column so as to accord with such a steering column design. The principal, operative part of a steering mechanism as defined below while referred to as a “steering column” may not be recognizable as such in the conventional sense; and need not be mounted relative to a fascia or dashboard as mentioned above. All such variations are within the scope of the present disclosure.

Moreover the steering set-up of the vehicle may include parts and sub-systems that do not in the literal sense form part of a steering column. To this end herein the term “steering mechanism” is intended to embrace all mechanically, electrically, electronically or electro-mechanically connected arrangements that convert driver or other steering inputs into the steering action of ground engaging members.

In a further optional refinement, the vehicle may include at least one receiver of transmitted vehicle guidance signals and at least one controller that converts received guidance signals to steering input commands that are input to the first steering servomechanism and/or the second steering servomechanism.

As a result, the vehicle may be arranged to operate in accordance with a remote guidance regime.

As an example of such an arrangement on very large farms the directional guidance of tractors may occur on the basis of command signals transmitted from an orbiting satellite that in turn may contain stored within a memory device a map of the field in which a tractor operates. Such an automatically guided vehicle does not require the input of an operator at all when performing field tasks, and instead maneuvers in dependence on data transmitted from the satellite and received by the vehicle-mounted signal receiver.

An arrangement of this kind could operate on the basis of “Global Positioning System” signals, or other signals created specifically for the farm in question.

Another example of use of a vehicle equipped with a signal receiver arises when performing operations such as ploughing or seeding in a very large field. In such a case if the field is of an essentially regular shape such as a rectangle a contractor may operate multiple tractors simultaneously in the field. As a result it may be possible to complete the field task very quickly (and thereby for example take advantage of favorable meteorological conditions, or the scheduling of use of the vehicles in question).

Since each of the tractors will complete essentially the same maneuvers as the others, albeit in each case following a line displaced to one side or the other across the width of the field compared with an adjacent tractor, it is not necessary to provide a driver in the cab of each tractor. On the contrary it may be possible for only one, “command” tractor to be operated by a driver, and for the others in the group to be driverless.

The command tractor may operate under the control of the driver or on some other basis (such as an automated guidance regime) and may transmit guidance commands via a transmitter to the other vehicles in the group. The latter would receive the commands and generate control commands for one or both of the steering servomechanisms. As a result the driverless tractors could for example copy the maneuvers of the “command” tractor, or could replicate them in a modified way that takes account of the lateral displacement or localized conditions in the portion of the field in which the driverless vehicles operate.

In yet a further variant all the tractors in a group could be driverless and could receive remotely generated guidance/steering commands. A supervisor could oversee operations of the tractors of the group from the edge of the field, or even from a remote location (using e.g. telemetry equipment such as video cameras coupled to transmitters and fitted to one or more of the tractors).

Preferably the amount of steering assistance is adjustable depending on at least one of the following signals:

-   -   vehicle speed or wheel speed     -   steering wheel angle     -   electric motor position (angle)     -   joystick position     -   steerable wheel alignment angle     -   torque on the steering column     -   hydraulic pressure in one or more hydraulic steering cylinder(s)     -   driver input torque on the steering wheel     -   electric motor supply current or voltage     -   guidance signals.

When referring to the alignment angle of steerable wheels in this context one may consider front steerable wheels (as are present in a conventional tractor); rear steerable wheels such as those commonly employed in a combine harvester; and/or an articulated vehicle frame arrangement, as used in a so-called bi-directional or articulated tractor, in which hydraulic cylinders cause articulation of front and rear parts of a vehicle frame. The present disclosure is applicable to all such types of steering set-up; and references herein to “steerable wheels” and similar components should be construed accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

There now follows a description of certain embodiments, by way of non-limiting example, with reference being made to the accompanying drawings in which:

FIG. 1 is a schematic, perspective view of parts of a vehicle, according to an embodiment of the present disclosure, embodying features as described herein;

FIG. 2 shows an example of a “human-machine interface” (HMI) that is suitable for use in a vehicle;

FIG. 3 is a perspective view showing the HMI of FIG. 2 installed in the cab fascia of an agricultural tractor;

FIG. 4 is a perspective view showing the location in the cab of a tractor of some further components forming part of the steering system;

FIG. 5a shows in plan view from above an example of a first maneuver (passing from a road into a field) that may be performed by a tractor, and FIG. 5b shows the status of the HMI of FIGS. 2 and 3 at such a time;

FIG. 6a shows an example of a second maneuver (carrying out a task involving passing along the field) that may be performed by the tractor of FIGS. 5a and 5b , and FIG. 6b shows the prevailing status of the HM during the maneuver;

FIGS. 7a and 7c show an example of a third maneuver (initiating and completing a headland turn) that may be performed by the tractor, and FIGS. 7b and 7d show the statuses of the HMI;

FIG. 8a shows an example of a fourth maneuver (returning from the field to a road) that the tractor may complete;

FIG. 8b shows the status of the HMI at such a time; and

FIG. 9 is a block diagram of an embodiment of a steering control system that may be employed within a steerable vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings a self-propelled vehicle in the form of a tractor 20 (FIGS. 3-8) according to certain embodiments of the present disclosure includes a rotatable steering column 21.

In the embodiment illustrated the steering column 21 takes the form of an elongate rod that over the major part of its length is solid and rigid.

The steering column 21 in the preferred embodiment shown interconnects at an upper end, inside the cab 22 of the tractor 20, a steering input member in the form of a conventional steering wheel 23 and at a lower end, inside the powertrain compartment of the tractor at its forward end, the control valve 24 of a hydraulic steering assistance sub-system that is described in more detail below.

In the certain embodiments, the steering wheel or another steering input member would be present, but it is possible to devise driverless versions of the vehicle in which it would not be strictly necessary to provide a steering input member. In practice however even in a version of the vehicle that is intended to be driverless a steering input member typically would be present in order to provide the option of driver-operation should this be desired.

The steering column 21 is journaled in one or more bearings at two or more locations along its length in order to permit it to rotate about its longitudinal axis. The bearings are omitted from FIG. 1 for ease of illustration, and may be of conventional designs.

The steering column 21 optionally may include any of a range of engineering features that are commonplace in such components. These include collapsible sections that absorb energy in the event of a crash accident, and articulated joints such as optional joint 42 that is visible in FIG. 1 permitting the transfer of rotational motion in a steering column that is not completely straight along its whole length.

The tractor 20 includes in the embodiment shown four ground-engaging members in the form of pairs of front (26) and rear (27) wheels (FIG. 5a ).

The front wheels 26 are steerable as a result of rotation of the steering column 21. To this end the steering column 21 is operatively connected at its forwardmost end 21 a to a series of steering linkage members that constitute a steering mechanism. The steering mechanism interconnects the steering column 21 and the front, steerable wheels 26 in a manner that converts rotational movement of the steering column 21 into rotations of the essentially upright wheels 26 about the caster (steering) axis that is a well-known parameter of steerable wheel design.

The vehicle 20 includes a first steering servomechanism in the form of the hydraulic steering assistance sub-system mentioned above.

This sub-system includes the hydraulic control valve that in certain embodiments is a double acting, bidirectional proportional valve having a rotary input to which the lowermost end 21 a of the steering column 21 is secured such that rotation of the steering column 21 clockwise and anti-clockwise causes movement of e.g. a valve spool to either side of a center (closed) position.

The valve 24 includes connected thereto in a per se known manner on an input side a pair of hydraulic feed lines 28, 29 that are in turn connected to output ports of a pump for pressurizing hydraulic fluid (e.g. oil) in the circuit constituted by the valve 24 and related components.

On an output side valve 24 connects by way of further hydraulic feed lines 31, 32 to a double acting, hydraulic cylinder 33.

Cylinder 33 is as illustrated mounted securely in the vehicle 20 in an orientation that under normal use of the vehicle is horizontal. At each end the cylinder 33 includes a respective extensible steering linkage arm 34, 36.

Each of the linkage arms 34, 36 terminates at a free end in a rose joint 37 or a similar fixing by which it secures to the stub axle of one of the steerable front wheels 26.

Rotation of the steering column as stated moves the spool of valve 24 away from its center position. This pilots pressurized hydraulic oil fed into the valve 24 via the lines 28, 29 in a manner causing simultaneous extension of one of the linkage arms 34, 36 outwardly from the cylinder 33 and retraction of the other to a location withdrawn inside the cylinder 33. This causes power-operated steering of the wheels 26 to occur, in a manner that is known per se.

The hydraulic steering assistance sub-system illustrated additionally includes return hydraulic fluid line 38 that interconnects the valve 24 and the pump for the purpose of recirculating hydraulic oil expelled from the cylinder 33 as a result of retraction of one or other of the linkage arms 34, 36.

As described above in the event of the first steering servomechanism ceasing to provide assistance the cylinder 33 in effect becomes a rigid transverse steering linkage member by reason of the trapping of a column of hydraulic fluid inside it. The cylinder therefore may transfer rotations of the steering column as steering movements of the wheels 26 even if e.g. the hydraulic fluid pump ceases operating.

The vehicle 20 also includes a second steering servomechanism in the form of an electric steering assistance sub-system constituted by a steering column rotary electric motor 39 and a controller in the form of an electronic control unit (ECU) 41.

The electric motor 39 in the embodiment shown is mounted with its axis of rotation extending transversely of the steering column 21. A pinion or other drive-transferring gear at the end of the output shaft of the motor engages a similar pinion that is connected to the steering column 21. Powered rotation of the output shaft causes powered assistance of the rotation of the steering column 21 in a per se known manner. The torque and the extent of rotation of the motor 39 are controlled in dependence on control commands generated in the ECU 41, that is operatively connected to the motor 39 e.g. by way of a CAN-BUS forming part of the control system of the tractor 20, or by any equivalent means.

The nature of the coupling between the output shaft of the motor 39 and the steering column 21 is such that in the event of the motor offering no assistance (for example if there is a component failure in the second steering servomechanism) rotation of the steering column 21 as a result of rotation of the steering wheel alone is not prevented.

The two servomechanisms described are associated with differing characteristics in terms of the steering assistance they provide.

Thus for example the hydraulic valve 24 and cylinder 33 amount to a so-called “non-reactive” assistance sub-system. By this is meant an arrangement in which the assistance force may be maintained at the same value regardless of the degree to which the steering wheel 23 is turned.

This means that considered on its own the first steering servomechanism of the vehicle does not provide any self-centering effect and instead is useful to maintain a constant steering angle. Thus in situations in which it is desired to steer a steady curve continuously with little or no driver input the controller (ECU) 41 may operate so that a relatively large proportion of the steering assistance power is provided by the hydraulic circuit constituting the first servomechanism, and a relatively small proportion by the second, electric servomechanism.

Similarly the first servomechanism described can provide a significant damping effect in the steering response of the vehicle (the degree of damping being inversely proportional to the tendency of the steering to be deflected e.g. by undulations in the surface on which the vehicle travels). Therefore when travelling in straight lines (for example when ploughing or sowing) again it may be desirable for the controller to ensure that a relatively large proportion of the assistance is provided by the hydraulic circuit constituting the first steering servomechanism.

It is possible to achieve a relatively low, or zero, proportion of assistance from the second, electric steering servomechanism by reducing the current supplied to the motor 39 in dependence on the signals generated in the controller (ECU) 41.

In other circumstances, such as when moving on roads, it may be preferable to increase the assistance provided by the second, electric steering servomechanism. It may be possible to devise embodiments in which adjustment of the relative amounts of steering assistance provided respectively by the first and second servomechanisms occurs by reducing the pump pressure seen at the actuator 33. For example, the controller (ECU) 41 may be communicatively coupled to the pump and configured to control the steering assistance provided by the actuator 33 by outputting control signals indicative of a hydraulic fluid pressure to the pump. In the certain tested embodiments, however, the assistance provided by the first, hydraulic servomechanism remains constant while the amount of assistance provided by the second, electric servomechanism is adjusted as stated in order to produce the desired effects.

At yet other times it may be desirable to operate with maximal assistance provided by both the servomechanisms, such as when wishing to convert quickly from full right steering lock to full left steering lock (or vice versa).

Examples of some modes of assistance that are as a result possible include but are not limited to the following:

“Effortless” sub-mode: the electric motor 39 (first servomechanism) provides a torque that almost exactly compensates the friction forces on the steering column. Therefore with a very low input force requirement (or even zero or almost zero if desired) the driver can steer the vehicle.

“Lock-to-lock” sub mode: the driver provides an initial rotary force input motion to the steering wheel 23, and thereafter does not need to provide any further torque input. The electric motor 39 moves the front wheels until the lock position is reached at the constant speed given by the driver. The assistance interrupts immediately in the event of the driver again grasping the steering wheel.

“Go to center mode”: This is similar to the “lock-to-lock” sub-mode, but the front wheel alignment stops adjusting when the wheels reach a designated center position.

The vehicle 20 includes a means for selecting the degree of assistance offered by at least one of the servomechanisms (i.e. preferably the second, electric servomechanism) between a minimum level (that might represent no assistance at all, depending on the precise design of the vehicle and the servomechanisms) and a maximum representing a safe performance limit of the servomechanism.

One form that such a means may take is the human-machine interface (HMI) panel 43 shown in FIGS. 2, 3 and 5 b-8 b.

The HMI panel 43 may be of a wide variety of possible designs. The basic functions of the panel 43 are:

-   -   selection of the steering assistance depending on the work         condition (headland, field, road, etc.)     -   selection of transition mode between different assistance levels         (i.e. manual, related to the HTS (headland turning sequence)         button; other vehicle functions; automatic)

The HMI by which selection of modes of operation, such as but not limited to those outlined above, may be made as stated can take a variety of forms. One desirable characteristic of such a panel when employed in an agricultural vehicle such as a tractor is that it is quick and simple to use. This is primarily for the reasons given above, namely that a tractor driver often must respond quickly to rapidly-changing circumstances while operating complicated sub-systems of a heavy, powerful vehicle. Simplicity and speed of operation therefore are often very important in the design of tractor sub-systems.

Also a tractor driver may have to work wearing gloves or other protective clothing that limits his dexterity. Ideally the panel 43 should be designed with such features in mind.

Different requirements however may arise in other types of vehicle, and for this reason among others the HMI panel 43 described herein is merely exemplary and is not limiting of the scope of the present disclosure.

HMI panel 43 includes a pair of mode selection buttons 44, 46 that if desired may be secured in an accessory panel 47. Each button 44, 46 lies adjacent an array of sub-mode indicator lamps 44 a, 44 b, 44 c, 44 d, 46 a, 46 b, 46 c, and beneath each button 44, 46 on the panel 47 is marked a respective legend indicating the circumstances under which a particular menu of steering assistance modes should be selected.

The legends shown are suitable for use in an agricultural tractor, and therefore read “HEADLAND” adjacent button 44 (which therefore is used to select steering assistance modes suitable for tractor turns in field headlands) and “FIELD/ROAD” adjacent button 46 (which therefore selects modes appropriate to driving on relatively smooth surfaces and/or when there is little need for significant turn assistance).

Each of the buttons is wired and/or is connected to ECU 41 such that pressing of one button 44, 46 automatically cancels any prevailing selection made using the other button. Each sequential press of one of the buttons causes the selection of the sub-modes indicated by the adjacent array of indicator lamps 44 a-d or 46 a-c in turn, such that the mode selection buttons may be used to “scroll” through the sequence of sub-modes until a desired sub-mode is selected.

The sub-mode indicator lamp of a selected sub-mode illuminates as selection occurs. An appropriate legend identifying each mode, as illustrated in FIG. 2, is marked adjacent each respective indicator lamp.

In addition to the foregoing, as described in more detail below, the selection of at least some modes may take place on an automatic basis.

FIG. 3 shows location of the HMI 43 of FIG. 2 in one exemplary position in the front dashboard 48 inside the cab 22 of a tractor 20. Other layouts and positions are of course possible within the scope of the present disclosure and will vary from one design of vehicle to another.

FIG. 4 further illustrates one way, of many, in which certain components as described herein may be located in the vehicle cab 22.

FIG. 4 shows a vehicle steering wheel 23 in a conventional location. A shroud that normally obscures the parts of the steering column 21 that lie inside the cab 22 has been removed to show one possible location for the motor 39 forming part of the second steering servomechanism.

Also visible in FIG. 4 is a joystick 49 that is provided in certain tractor designs in order to provide control for various functions of the tractor 20.

The joystick is a second driver-operated steering input member that is electronically coupled and is configurable (e.g. as a result of pressing of an actuation button) to act as an input member via which the tractor operator may input steering commands.

The joystick is useful in particular when the vehicle operator is performing maneuvers requiring him/her to look out of the rear window 51 of the cab 22. Controlling the steering of the tractor 20 is considerably easier at such a time when the joystick is used instead of the steering wheel 23. In some tractors 20 an operator's seat 52 is capable of swiveling to make it comfortable for the operator to control the tractor 20 while looking out of the rear window 51.

Referring now to FIGS. 5-8 a number of options are illustrated for selecting the sub-modes that are available in the exemplary tractor 20 described above. As indicated elsewhere herein, the list of sub-modes described and their grouping as sequences are not intended to be limiting, and many other combinations of sub-modes of steering control are possible.

In FIG. 5a the tractor 20 is shown travelling on a relatively smooth road surface 53 just before turning in to a field 54 via a field gateway 56 that marks a transition from one type of operation (driving on road) to another (e.g. spreading, spraying, seeding, ploughing, harrowing, rolling or otherwise treating the soil of the field).

While driving on the road the operator of the tractor 20 selects the “FIELD/ROAD” menu of sub-modes by pressing button 46 of HMI 43 as signified in FIG. 5 b.

In the illustrated embodiment this results in the selection of the sub-mode “Transport” that is signified by illumination of indicator lamp 46 a.

The “Transport” sub-mode applies steering assistance, using the first and second steering servomechanisms under control of the ECU 41, such that the steering is reactive and self-centering. The aim of the “Transport” sub-mode is to replicate as far as possible in a tractor weighing several tons the feeling of steering a passenger car on the road 53. This assists the tractor operator to respond to road situations in a similar manner to the other road users nearby.

Selection of one sub-mode via the HMI 43 inhibits the selection of all other sub-modes, that would as a result need to be selected specifically in order to take effect.

However in the preferred embodiment shown selection of “Transport” mode in particular may occur automatically when the tractor 20 moves on a road. Automatic selection of “Transport” mode may take place for example whenever the forward speed of the tractor exceeds a chosen threshold (such as but not limited to 25 km/h) signifying on-road driving. The ECU 41, that preferably is programmable, may include an algorithm that achieves this effect.

Once the tractor 20 is in the field 54 the operator may as desired use the mode selection button 46 as many times as desired in order to “scroll” the menu of available sub-modes and select the one that most accurately suits the field conditions and the tasks that the tractor must fulfil.

Thus the operator may maintain the selection of the “Transport” sub-mode (for example if the field is relatively smooth and flat, as is often the case in certain types of livestock pasture and fields that are cultivated for forage growing), or he/she may select a “Damp” sub-mode (in which damping of the steering as explained herein is at a maximal level) or an “Effortless” sub-mode in which the effort to rotate the steering wheel is very low, or perhaps even zero.

The “Damp” sub-mode as indicated is particularly suitable when operating in rutted or furrowed ground in which it would otherwise require very considerable effort on the part of the operator to make the tractor 20 maintain a chosen course. Also the “Damp” mode would be suitable if it was necessary to follow a continuously curved course, representing for example a curved field margin.

The effortless sub-mode is suitable for making headland operations faster than would otherwise be the case and with a lower effort required on the part of the vehicle operator.

FIG. 6b shows the “Damp” sub-mode button 46 b illuminated by way of illustration.

While performing operations in a field the operator may in addition select a further operational mode, in which the joystick 49 if fitted to the tractor 20 becomes active as the steering input member. In the illustrative embodiment described selection of this mode may take place through depressing of a button on the joystick 49 itself, but in other embodiments alternative ways of selecting the sub-mode may be available. Examples include but are not limited to use of one or a combination of the mode selection buttons 44, 46 or another button that may also form part of the HMI. Selection of a reverse gear or the activation of a rear-mounted implement may also be used to initiate steering input via the joystick 49.

In FIG. 7a the tractor 20 has temporarily ceased field operations in order to permit turning in a headland 57 at an end of the field 54.

Normally in the headland any implement or other ground-treating accessory of the tractor 20 is deactivated (e.g. by raising of the implement out of engagement with the soil, by closing off seed coulters, by switching off spray pumps and so on). The requirement of the tractor often then becomes one of maximum maneuverability in order to allow it to turn as smoothly, safely and quickly as possible in the headland margin.

When entering a headland therefore the operator of the tractor 20 may press the “HEADLAND” mode selection button 44 that in the embodiment shown would result in selection of the first of the headland sub-modes (i.e. “Damp” in the illustrated example).

The “Damp” sub-mode available via the HEADLAND menu may be the same as the “Damp” sub-mode available through pressing the “FIELD/ROAD” mode selection button, or it may result in the operation of a different program that causes different combinations of the damping effects available from the two steering servomechanisms.

The operator may also select an “Effortless” sub-mode in which the steering becomes as light as possible (i.e. maximum assistance is provided using the two steering servomechanisms); a “Back to center” sub-mode, in which the self-centering is maximized; and a “Lock-to-lock” mode in which movement of the steering wheel when at one extreme of steering lock causes assisted rotation to the opposite lock setting. This last mentioned mode may be of help for example when the headland is particularly confined.

FIG. 7b shows the “Effortless” sub-mode indicator lamp in an illuminated state, signifying selection of that sub-mode.

In some tractors and other agricultural vehicles the electronics and/or the software are programmable for the purpose of recording a sequence of control actions. One example of when this is beneficial is when performing a turn in the headland of an essentially rectangular field during operations that rely on use of an implement.

On the occasion of a first turn of this kind that the vehicle makes after entering such a field the tractor operator may press a “PROGRAM” or “RECORD” button before carrying out the headland turn steps (i.e. raising the implement attached to the tractor, selecting a chosen low gear ratio, adjusting the engine governor and operating the steering wheel to perform the turn before re-engaging the implement and selecting the appropriate gear and governor settings for continuing field work). Pressing of the PROGRAM or RECORD button (assuming one is present) causes the vehicle control software to store the sequence of steps so that the headland turns may be reliably performed each time the vehicle reaches an end of the field.

The apparatus and operation are compatible with such an arrangement and indeed the selection of particular modes and sub-modes as described above may if desired be treated as recordable steps that can form part of a sequence as described above.

FIG. 7c illustrates the tractor 20 resuming field operations after completion of a headland turn. In certain embodiments, the tractor operator presses the “FIELD/ROAD” button in order to effect a transition back to the same sub-mode of assistance that prevailed before initiation of the headland turn. Thus in FIG. 7d the “Damp” sub-mode indicator lamp 46 b is illuminated. This lamp 46 b also may be arranged to flash during the headland turn in order to remind the operator of the sub-mode to which the tractor steering would return following pressing of the mode selection button 46 at the end of the turn.

FIG. 8a shows the tractor leaving the field 54 and returning to the road 53 at the end of a period of work. The operator may select the “Transport” sub-mode using the button 46 at this time; or he/she may simply permit automatic selection of this mode to occur as the forward speed of the tractor exceeds the chosen threshold value.

In addition to the foregoing modes, as explained the tractor 20 may be equipped with a so-called “autoguidance” device (such as a Global Positioning System receiver, or another type of receiver of steering and/or navigation signals). Also as explained above such signals may derive from satellites in Earth orbit, other vehicles (such as other tractors working nearby) or even fixed transmitters. When so equipped the tractor 20 may maneuver without need for operation of the steering input devices such as steering wheel 23 or joystick 49. Such devices therefore may be dispensed with, although preferably at least the steering wheel 23 would be retained.

FIG. 9 is a block diagram of an embodiment of a steering control system 100 that may be employed within a steerable vehicle. In the illustrated embodiment, the steering control system 100 includes a steering mechanism 102 having a rotatable steering column 21 configured to control a steering angle of at least one ground-engaging member of the steerable vehicle. The at least one ground-engaging member may include an element (e.g., wheel, track, etc.) that engages the ground and is steerable by the steering control system. In the illustrated embodiment, the at least one ground-engaging member includes a pair of front wheels 26 (e.g., a left front wheel 104 and a right front wheel 106). However, in other embodiments, the at least one ground-engaging member may include more or fewer front wheels and/or one or more rear wheels (e.g., in addition to the front wheels or as an alternative to the front wheels). In further embodiments, the at least one ground-engaging member may include at least one track (e.g., one or more front tracks and/or one or more rear tracks). Each ground-engaging member may be coupled to a chassis of the steerable vehicle by a knuckle or any other suitable connection system.

In the illustrated embodiment, the steering control system 100 includes a first steering servomechanism 108 configured to adjust the steering angle of the front wheels 104 and 106 based on a rotation angle of the steering column 21. The first steering servomechanism 108 includes a hydraulic steering servomechanism 110. The hydraulic steering servomechanism 110 includes a hydraulic steering valve 24 coupled to the rotatable steering column 21 and a hydraulic cylinder 33 fluidly coupled to the hydraulic steering valve 24 by first and second hydraulic lines 31 and 32. The hydraulic steering valve 24 is configured to control hydraulic fluid flow in the hydraulic lines 31 and 32 based on the rotational angle of the rotatable steering column 21, thereby driving the hydraulic steering cylinder 33 to adjust the steering angle of the front wheels 104 and 106. In the illustrated embodiment, a first steering linkage arm 34 of the hydraulic cylinder 33 is coupled to the front left wheel 104 by a respective joint 37, and a second steering linkage arm 36 is coupled to the front right wheel 106 by a respective joint 37.

As illustrated, the hydraulic steering valve 24 is fluidly coupled to a hydraulic pump 112 by hydraulic lines 28 and 29. Rotation of the rotatable steering column 21 to the left induces the hydraulic steering valve 24 to flow pressurized hydraulic fluid from the pump 112 to the first hydraulic line 31. The pressurized fluid within the first hydraulic line 31 induces the first and second steering linkage arms 34 and 36 to move to the right, thereby rotating the left and right front wheels 104 and 106 to the left. Conversely, rotation of the rotatable steering column 21 to the right induces the hydraulic steering valve 24 to flow pressurized hydraulic fluid from the pump 112 to the second hydraulic line 32. The pressurized fluid within the second hydraulic line 32 induces the first and second steering linkage arms 34 and 36 to move to the left, thereby rotating the left and right front wheels 104 and 106 to the right. While the hydraulic steering servomechanism 110 includes a single hydraulic steering cylinder 33 in the illustrated embodiment, in other embodiments, the hydraulic steering servomechanism may include additional hydraulic steering cylinders (e.g., a hydraulic steering cylinder configured to drive rear wheel(s) to rotate).

In the illustrated embodiment, the steering control system 100 includes a second steering servomechanism 114 having an electric power steering servomechanism 116. The electric power steering servomechanism 116 includes a motor 39 (e.g., electric motor) configured to control a torque on the rotatable steering column 21 to establish a steering assistance characteristic. An output shaft of the electric motor may be coupled to the rotatable steering column by a gear assembly or other suitable connection. Accordingly, rotation of the output shaft of the electric motor urges or drives the rotatable steering column to rotate. For example, as discussed in detail below, in response to engagement of automatic guidance, the motor 39 may drive the rotatable steering column 21 to steer the steerable vehicle along a target route. In addition, while the rotatable steering column is driven to rotate by the operator, the motor may apply a torque to the rotatable steering column to establish the steering assistance characteristic.

As used herein, steering assistance characteristic refers to an induced tactile feedback within the steering wheel 23 (e.g., induced by the electric motor 39) during operator control of the steerable vehicle (e.g., while the operator is in contact with the steering wheel and using the steering wheel to control the direction of travel of the steerable vehicle). Accordingly, controlling the steering assistance characteristic controls the torque felt by the operator through the steering wheel. As discussed in detail below, the steering assistance characteristic may be controlled based at least in part on a selected programmed mode of operation and/or sub-mode.

In the illustrated embodiment, the hydraulic steering valve 24 is coupled to an end of the rotatable steering column 21, opposite the steering wheel 23. In addition, the motor 39 is coupled to the rotatable steering column 21 at a location between the steering wheel 23 and the hydraulic steering valve 24. Accordingly, the motor attachment location is different than the hydraulic steering valve attachment location. In alternative embodiments, the motor and/or the hydraulic steering valve may be positioned at other locations along the rotatable steering column (e.g., such that the motor and the hydraulic steering valve are positioned at different locations along the rotatable steering column).

In the illustrated embodiment, the steering control system 100 includes a controller 118 (e.g., which may correspond to the ECU 41 disclosed above). The controller 100 is communicatively coupled to the motor 39 and to the pump 112. Accordingly, the controller 118 may output control signals to the motor 39, thereby causing the motor to control the torque applied to the rotatable steering column 21. For example, the controller 118 may control the steering assistance characteristic by outputting control signals indicative of a magnitude and a direction of the torque to influence steering of the steerable vehicle. In addition, the controller 118 may output control signals to the pump 112, thereby instructing the pump 112 to control hydraulic fluid pressure to the hydraulic steering servomechanism 110.

In the illustrated embodiment, the steering control system 100 also includes a hand controller 120 (e.g., which may correspond to the joystick 49 disclosed above) communicatively coupled to the controller 118. The hand controller 120 is configured to output a signal indicative of a position of the hand controller 120. The controller 118, in turn, is configured to instruct the motor 39 to drive the rotatable steering column 21 to rotate based on the position of the hand controller 120. Accordingly, the hand controller may be used to steer the steering vehicle. For example, in certain embodiments, the steering wheel may be positioned on a first side (e.g., front side) of the cab of the steerable vehicle, and the hand controller 120 may be positioned on a second side (e.g., rear side) of the cab, opposite the first side. In such embodiments, the hand controller may be used to steer the steerable vehicle while the operator is facing away from the steering wheel. In certain embodiments, the controller 118 may be configured to instruct the motor 39 to drive the steering column to rotate through an angle corresponding to the position of the hand controller 120. For example, the controller may instruct the motor to drive the rotatable steering column to rotate through a small angle in response to movement of the hand controller through a range of motion while the hand controller is proximate to a center position, and the controller may instruct the motor to drive the rotatable steering column to rotate through a large angle in response to movement of the hand controller through the range of motion while the hand controller is proximate to an end-of-stroke position. While the steering control system includes a hand controller in the illustrated embodiment, in other embodiments, the hand controller may be omitted.

In the illustrated embodiment, the steering control system 100 includes a steering angle sensor 122 configured to output a sensor signal indicative of the steering angle of the front wheels 104 and 106. However, in embodiments in which the at least one ground-engaging member includes one or more other wheels/tracks and/or one or more additional wheels/tracks, the steering angle sensor 122 may be configured to output a sensor signal indicative of the steering angle of such wheels/tracks. In certain embodiments, the steering angle sensor 122 may be integrated within the hydraulic cylinder 33 and configured to output a sensor signal indicative of the position of the first steering arm linkage 34 and/or the second steering arm linkage 36. In further embodiments, the steering angle sensor 122 may be mounted to a frame of the steerable vehicle and configured to monitor an orientation of the at least one ground-engaging member. The steering angle sensor 122 may include any suitable sensor configured to monitor the steering angle of the at least one ground-engaging member, such as a Hall-effect sensor, a linear variable differential transformer (LVDT), a linear potentiometer, a rotatory potentiometer, an infrared sensor, an ultrasonic sensor, another suitable type of sensor, or a combination thereof. As illustrated, the steering angle sensor 122 is communicatively coupled to the controller 118, thereby enabling the controller to receive the sensor signal indicative of the steering angle of the at least one ground-engaging member.

In the illustrated embodiment, the steering control system 100 includes a torque sensor 124 configured to output a sensor signal indicative of the torque applied to the rotatable steering column 21. The torque sensor 21 may include a strain gauge, a surface acoustic wave (SAW) device, a magnetoelastic torque sensor, another suitable type of torque sensor, or a combination thereof. As illustrated, the torque sensor 124 is communicatively coupled to the controller 118, thereby enabling the controller to receive the sensor signal indicative of the torque applied to the rotatable steering column 21.

Furthermore, in the illustrated embodiment, the steering control system 100 includes a spatial locating device 126, which is mounted to the steerable vehicle and configured to determine a position and, in certain embodiments, a velocity of the steerable vehicle. The spatial locating device 126 may include any suitable system configured to measure and/or determine the position of the steerable vehicle, such as a GPS receiver, for example. In certain embodiments, the spatial locating device 126 is configured to output a sensor signal indicative of the speed of the steerable vehicle. As illustrated, the spatial locating device 126 is communicatively coupled to the controller 118, thereby enabling the controller to receive the sensor signal indicative of the speed of the steerable vehicle. In certain embodiments, the spatial locating device may be configured to output signals indicative of vehicle position to the controller, and the controller may determine the speed of the steerable vehicle based on the signals.

In the illustrated embodiment, the steering control system 100 also includes a wheel speed sensor 128 configured to output a sensor signal indicative of a speed of the at least one ground-engaging member. The wheel speed sensor 128 may include an optical sensor, an infrared sensor, a potentiometer, another suitable type of wheel speed sensor, or a combination thereof. As illustrated, the wheel speed sensor 128 is communicatively coupled to the controller 118, thereby enabling the controller to receive the sensor signal indicative of the speed of the at least one ground-engaging member. While the wheel speed sensor 128 is configured to monitor the speed of the left front wheel 104 in the illustrated embodiment, in other embodiments, the wheel speed sensor may be configured to monitor the speed of another suitable wheel, and/or the steering control system may include multiple wheel speed sensors to monitor the speeds of multiple wheel.

While the illustrated embodiment includes a steering angle sensor 122, a torque sensor 124, a spatial locating device 126, and a wheel speed sensor 128, in alternative embodiments, the steering control system may include more or fewer sensors. For example, in certain embodiments, at least one of the steering angle sensor, the torque sensor, the spatial locating device, and the wheel speed sensor may be omitted. Furthermore, in certain embodiments, the steering control system may include other and/or additional sensors, such as a steering wheel angle sensor, a motor position sensor, a hydraulic pressure sensor (e.g., to monitor the pressure of hydraulic fluid within the hydraulic cylinder), a motor supply current and/or voltage sensor, or a combination thereof.

In certain embodiments, the controller 118 is an electronic controller having electrical circuitry configured to process data from the sensors and/or other components of the steering control system 100. In the illustrated embodiment, the controller 118 include a processor, such as the illustrated microprocessor 130, and a memory device 132. The controller 118 may also include one or more storage devices and/or other suitable components. The processor 130 may be used to execute software, such as software for controlling the motor 39, software for controlling the pump 112, and so forth. Moreover, the processor 130 may include multiple microprocessors, one or more “general-purpose” microprocessors, one or more special-purpose microprocessors, and/or one or more application specific integrated circuits (ASICS), or some combination thereof. For example, the processor 130 may include one or more reduced instruction set (RISC) processors.

The memory device 132 may include a volatile memory, such as random access memory (RAM), and/or a nonvolatile memory, such as read-only memory (ROM). The memory device 132 may store a variety of information and may be used for various purposes. For example, the memory device 132 may store processor-executable instructions (e.g., firmware or software) for the processor 130 to execute, such as instructions for controlling the motor 39, instructions for controlling the pump 112, and so forth. The storage device(s) (e.g., nonvolatile storage) may include ROM, flash memory, a hard drive, or any other suitable optical, magnetic, or solid-state storage medium, or a combination thereof. The storage device(s) may store data (e.g., threshold values, etc.), instructions (e.g., software or firmware for controlling the motor and/or the pump, etc.), and any other suitable data.

In the illustrated embodiment, the at least one ground-engaging member is (e.g., the front wheels are) not coupled to the steering column 21 by a mechanical linkage. Accordingly, the only component of the steering control system 100 configured to drive the at least one ground-engaging member to rotate is the hydraulic steering servomechanism. As previously discussed, the hydraulic steering servomechanism 110 includes the hydraulic steering valve 24 and the hydraulic cylinder 33. The hydraulic steering valve 24 is configured to control the flow of hydraulic fluid to the hydraulic cylinder based on the rotation angle of the rotatable steering column 21, thereby causing the hydraulic cylinder to adjust the steering angle of the at least one ground-engaging member. Furthermore, the motor 39 of the electric power steering servomechanism 116 is configured to control a torque on the rotatable steering column to establish a steering assistance characteristic. The controller 118 is configured to control the steering assistance characteristic by outputting control signals indicative of a magnitude and a direction of the torque to the motor 39 to influence steering of the steerable vehicle.

Because the hydraulic steering valve 24 is coupled to the steering column 21, the hydraulic steering valve 24 may influence the tactile feedback through the steering wheel 23. For example, an operator may apply a first torque to the steering wheel sufficient to transition the hydraulic steering valve between a first position that directs hydraulic fluid to one end of the hydraulic cylinder and a second position that directs hydraulic fluid to the other end of the hydraulic cylinder. In addition, an operator may apply a second torque sufficient to transition the hydraulic valve between two positions that direct the hydraulic fluid to the same end of the hydraulic cylinder. In certain embodiments, the first torque may be greater than the second torque. Accordingly, the tactile feedback through the steering wheel may vary throughout the rotational range of motion of the steering wheel. In certain embodiments, the controller 118 (e.g., in each of the programmed modes and/or sub-modes disclosed below) may be configured to control the steering assistance characteristic to compensate for the tactile feedback caused by the hydraulic steering valve (e.g., the variation in torque as the steering wheel rotates through the range of motion). As a result, the controller 118 may cause a desired/target tactile feedback to be induced within the steering wheel (e.g., a tactile feedback without the perceived influence of the hydraulic steering valve).

In the illustrated embodiment, the HMI panel 43 is communicatively coupled to the controller 118. The HMI panel 43 is configured to receive input commands indicative of selection of one of a set of programmed modes of operation (e.g., of the second servomechanism 114). For example, as discussed above with reference to FIGS. 2-8 b, the HMI panel may include one or more buttons configured to enable an operator to select a programmed mode and a sub-mode. In certain embodiments, the set of programmed modes includes a first programmed mode associated with steering during movement of the steerable vehicle within a field headland, and a second programmed mode associated with steering during movement of the steerable vehicle within a field and along a road. Furthermore, in certain embodiments, the first programmed mode includes a steering feedback sub-mode, a torque-free sub-mode, an automatic steering centering sub-mode, and a lock-to-lock assistance sub-mode. In addition, the second programmed mode may include a steering feedback sub-mode, an automatic steering centering sub-mode, and a torque-free sub-mode.

While the steering feedback sub-mode is selected, the controller 118 may control the electric power steering servomechanism 116 to simulate the feel of a mechanical steering system (e.g., a mechanical connection between the rotatable steering column and the at least one ground-engaging member). For example, the controller 118 may receive a sensor signal from the steering angle sensor 122 indicative of the steering angle, a sensor signal from the torque sensor 124 indicative of the torque on the rotatable steering column 21, a sensor signal from the spatial locating device 126 indicative of the speed of the steerable vehicle, a sensor signal from the wheel speed sensor 128 indicative of the speed of the at least one ground-engaging member, or a combination thereof, among other sensor signal(s). The controller 118 may then determine a target torque on the rotatable steering column 21 that simulates the feel of a mechanical steering system. The controller 118 may then output control signals to the motor 39 indicative of a magnitude and a direction of the target torque based at least in part on the sensor signal(s) to influence the steering of the steerable vehicle. For example, during operation of the steerable vehicle, the controller may control the motor 39 such that the torque on the rotatable steering column is substantially equal to the target torque.

The controller 118 may determine the magnitude and the direction of the target torque based at least in part on the steering angle and/or the speed of the steerable vehicle/at least one ground-engaging member. For example, the magnitude of the target torque for a larger steering angle may be greater than the magnitude of the target torque for a smaller steering angle. In addition, the magnitude of the target torque for a higher steerable vehicle/ground-engaging member speed may be greater than the magnitude of the target torque for a lower steerable vehicle/ground-engaging member speed. In certain embodiments, the controller may also be configured to determine the magnitude and the direction of the target torque based at least in part on hydraulic pressure within the hydraulic cylinder, among other factors.

While the torque-free sub-mode is selected, the controller 118 may instruct the motor 39 to apply no torque to the rotatable steering column 21 (e.g., by deactivating the motor 39). Accordingly, the operator may not receive any induced tactile feedback through the steering wheel 23 (e.g., the operator may experience the tactile feedback from the hydraulic steering valve and/or other components, such as bearings, coupled to the rotatable steering column). In certain embodiments, the controller 118 may control the motor 39 to compensate for the torque applied to the rotatable steering column 21 by the hydraulic steering valve 24 and/or other components, such as bearing, coupled to the rotatable steering column. For example, the controller 118 may control the motor 39 such that the magnitude of the torque on the rotatable steering column (e.g., as measured by the torque sensor 124) is substantially zero.

While the automatic centering sub-mode is selected, the controller 118 may control the motor 39 to urge or drive the rotatable steering column 21 toward a center position associated with the at least one ground-engaging member being straight (e.g., not turned). For example, while an operator is in contact with the steering wheel 23, the controller 118 may instruct the motor 39 to apply a torque to the rotatable steering column 21 to urge the steering column 21 toward the center position, thereby simulating the feel of operating a vehicle with self-centering ground-engaging member(s) (e.g., due to the geometry of the suspension, the configuration of the steering system, etc.). In addition, if the operator releases the steering wheel 23, the controller 118 may instruct the motor 39 to drive the steering column 21 to the center position, thereby causing the at least one ground-engaging member to rotate to a straight (e.g., not turned) position. Accordingly, upon releasing the steering wheel 23, the steerable vehicle transitions toward a straight path. In certain embodiments, a steering wheel angle sensor may be utilized to enable the controller to determine the magnitude of the torque (e.g., the magnitude of the torque applied by the motor may be substantially zero while the steering column is in the center position, and in certain embodiments, the magnitude of the torque may decrease as the steering column approaches the center position) and the direction of the torque (e.g., toward the center position).

In certain embodiments, while the automatic centering sub-mode is selected, the controller 118 may control the motor 39 to drive the rotatable steering column 21 toward the center position only upon rotation of the rotatable steering column by the operator (e.g., via the steering wheel). For example, in response to rotation of the rotatable steering column 21 toward the center position (e.g., as determined based on feedback from a steering wheel angle sensor, from the steering angle sensor 122, the torque sensor 124, etc.), the controller 118 may control the motor 39 to drive the steering column 21 to the center position, thereby causing the at least one ground-engaging member to rotate to a straight (e.g., not turned) position.

While the lock-to-lock assistance sub-mode is selected, the controller 118 may control the motor 39 to drive the rotatable steering column 21 to rotate toward a maximum rotational extent in response to an operator rotating the rotatable steering column 21 in the direction of the maximum rotational extent. For example, the controller may detect a direction of rotation of the rotatable steering column (e.g., based on feedback from a steering wheel angle sensor, from the steering angle sensor 122, from the torque sensor 124, etc.). Upon detection of the direction of rotation, the controller may control the motor to drive the rotatable steering column in the direction of rotation until the rotatable steering column reaches the maximum rotational extent (e.g., associated with the maximum rotational extent of the at least one ground-engaging member). The lock-to-lock assistance sub-mode may facilitate steering the steerable vehicle through headland turns.

In certain embodiments, the controller may automatically select the programmed mode and/or the sub-mode based on feedback from one or more sensors. For example, in certain embodiments, the controller may automatically select the steering feedback sub-mode or the automatic steering centering sub-mode upon determining that the speed of the steerable vehicle and/or the at least one ground-engaging member exceeds a threshold speed. Furthermore, in certain embodiments, the controller may automatically select the torque-free sub-mode upon determining that the measured torque on the rotatable steering column exceeds a threshold torque.

In certain embodiments, the controller is configured to engage automatic guidance (e.g., in response to receiving instructions from the HMI panel 43). In such embodiments, the controller 118 is configured to output control signals to the motor 39 to cause the motor to drive the rotatable steering column 21 to steer the steerable vehicle along a target route in response to engagement of automatic guidance. While the automatic guidance is engaged, the operator does not contact the steering wheel 23, thereby enabling the motor 39 to drive the rotatable steering column 21 to rotate. However, the controller 118 is configured to disengage the automatic guidance in response to receiving a sensor signal from the torque sensor 124 indicative of a magnitude of the torque exceeding a threshold torque. For example, while the operator is not contacting the steering wheel 23 during automatic guidance, the torque measured by the torque sensor 124 may be below the threshold torque. However, when an operator contacts the steering wheel 23, the operator may at least partially block rotation of the steering wheel 23, thereby inducing a torque within the rotatable steering column 21 greater than the threshold torque. Accordingly, when the operator contacts the steering wheel 23, the automatic guidance may be disengaged.

While control of (e.g., application of torque to) the rotatable steering column 21 is disclosed above, in certain embodiments, the hand controller may include an actuator configured to urge and/or drive the hand controller to move (e.g., rotate). For example, while the steering feedback sub-mode is selected, the controller may control the actuator to simulate the feel of a mechanical steering system. In addition, while the automatic centering sub-mode is selected, the controller may control the actuator to urge or drive the hand controller toward a center position. Furthermore, while the lock-to-lock assistance sub-mode is selected, the controller may control the actuator to drive the hand controller toward a maximum extent in response to an operator moving the hand controller in the direction of the maximum extent.

In alternative embodiments (e.g., the embodiment(s) disclosed above with reference to FIGS. 1-8 b), the at least one ground-engaging member is (e.g., the front wheels are) coupled to the steering column by a mechanical linkage. In such embodiments, the sensors described above with regard to FIG. 9 may be utilized to facilitate control of the rotatable steering column. For example, while the transport sub-mode is selected (e.g., as described above with reference to FIGS. 5a and 5b ), the controller 118 may receive a sensor signal from the steering angle sensor 122 indicative of the steering angle, a sensor signal from the torque sensor 124 indicative of the torque on the rotatable steering column 21, a sensor signal from the spatial locating device 126 indicative of the speed of the steerable vehicle, a sensor signal from the wheel speed sensor 128 indicative of the speed of the at least one ground-engaging member, or a combination thereof, among other sensor signal(s). The controller 118 may then determine a target torque on the rotatable steering column 21 that establishes a reactive and self-centering steering feel. The controller 118 may then output control signals to the motor 39 and/or the hydraulic pump 112 based at least in part on the sensor signal(s) to establish the target torque, thereby influencing the steering of the steerable vehicle.

Furthermore, while the damp sub-mode is selected (e.g., as described above with reference to FIGS. 6a and 6b ), the controller 118 may control the motor 39 and/or the pump 112 to damp rotation of the steering column 21 (e.g., caused by the at least one ground-engaging member engaging variations in the ground surface). For example, the controller 118 may instruct the pump to reduce hydraulic fluid pressure to the hydraulic cylinder 33, thereby enabling the hydraulic system to act as a damper. In addition, the controller may control the motor 39 to apply a torque to the rotatable steering column 21 in an opposite direction of an induced torque/rotation (e.g., a torque/rotation induced by the at least one ground-engaging member engaging variations in the ground surface). For example, the controller 118 may determine a target torque based at least in part on sensor signal(s) from the steering angle sensor 122 and/or the torque sensor 124. The controller 118 may then output control signals indicative of the magnitude and the direction of the target torque to influence steering of the steerable vehicle.

In addition, while the effortless sub-mode is selected (e.g., as described above with reference to FIGS. 7a and 7b ), the controller 118 may control the pump 112 and/or the motor 39 to provide significant assistance to the operator. For example, the controller 118 may instruct the pump 112 to output hydraulic fluid at a maximum capacity. In addition, the controller 118 may control the motor 39 such that the magnitude of the torque on the rotatable steering column 21 (e.g., as measured by the torque sensor 124) is substantially zero, or as low as the motor 39 is capable of establishing.

While the lock-to-lock sub-mode is selected, the controller 118 may control the motor 39 to drive the rotatable steering column 21 to rotate toward a maximum rotational extent in response to an operator rotating the rotatable steering column 21 in the direction of the maximum rotational extent. For example, the controller may detect a direction of rotation of the rotatable steering column (e.g., based on feedback from a steering wheel angle sensor, from the steering angle sensor 122, from the torque sensor 124, etc.). Upon detection of the direction of rotation, the controller may control the motor to drive the rotatable steering column in the direction of rotation until the rotatable steering column reaches the maximum rotational extent (e.g., associated with the maximum rotational extent of the at least one ground-engaging member).

Furthermore, while the “go to center” sub-mode is selected, the controller 118 may control the motor 39 to drive the rotatable steering column 21 toward a center position associated with the at least one ground-engaging member being straight (e.g., not turned). For example, in response to operator rotation of the rotatable steering column 21 toward the center position (e.g., as determined based on input from a steering wheel angle sensor, from the steering angle sensor 122, the torque sensor 124, etc.), the controller 118 may control the motor 39 to drive the rotatable steering column 21 to the center position, thereby causing the at least one ground-engaging member to rotate to a straight (e.g., not turned) position.

In certain embodiments, any of the features disclosed above with reference to FIG. 9 may be utilized within the steering system/steerable vehicle of the embodiment(s) disclosed above with reference to FIGS. 1-8 b. For example, the steering angle sensor 122 may be utilized to monitor the steering angle of at least one ground-engaging member disclosed above with reference to FIGS. 1-8 b. In addition, the torque sensor 124 may be utilized to monitor the torque applied to the rotatable steering column disclosed above with reference to FIGS. 1-8 b. Furthermore, any of the features disclosed above with reference to FIGS. 1-8 b may be utilized within the steering control system disclosed above with reference to FIG. 9. For example, any suitable programmed mode and/or sub-mode disclosed above with reference to FIGS. 1-8 b may be implemented within the controller disclosed above with reference to FIG. 9.

The listing or discussion of an apparently prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge. 

The invention claimed is:
 1. A steerable vehicle, comprising: a steering mechanism having a rotatable steering column; a first steering servomechanism comprising a hydraulic steering servomechanism, wherein the hydraulic steering servomechanism comprises a hydraulic steering valve coupled to the rotatable steering column and at least one hydraulic steering cylinder fluidly coupled to the hydraulic steering valve by hydraulic lines, and wherein the hydraulic steering valve is configured to control a hydraulic flow in the hydraulic lines based on a rotational angle of the rotatable steering column to drive the at least one hydraulic steering cylinder to adjust a steering angle of at least one ground-engaging member of the steerable vehicle; a second steering servomechanism comprising an electric power steering servomechanism, wherein the electric power steering servomechanism comprises a motor configured to control a torque on the rotatable steering column to establish a steering assistance characteristic; a controller configured to control the steering assistance characteristic by outputting control signals indicative of a magnitude and a direction of the torque to influence steering of the steerable vehicle; and a human-machine interface (HMI) configured to receive input commands indicative of selection of one of a plurality of programmed modes of operation of the second steering servomechanism; wherein the at least one ground-engaging member is not coupled to the rotatable steering column by a mechanical linkage; wherein a first programmed mode of operation of the plurality of programmed modes of operation comprises steering during movement of the steerable vehicle within a field headland, and a second programmed mode of operation of the plurality of programmed modes of operation comprises steering during movement of the steerable vehicle within a field and along a road; wherein the first programmed mode of operation comprises a steering feedback sub-mode, a torque-free sub-mode, an automatic steering centering sub-mode, and a lock-to-lock assistance sub-mode; and wherein the second programmed mode of operation comprises a steering feedback sub-mode, an automatic steering centering sub-mode, and a torque-free sub-mode.
 2. The steerable vehicle of claim 1, comprising a steering wheel mechanically coupled to the rotatable steering column.
 3. The steerable vehicle of claim 1, wherein the controller is configured to control the steering assistance characteristic based at least on a speed of the steerable vehicle, a speed of the at least one ground-engaging member, the rotational angle of the rotatable steering column, a position of the motor, a position of a joystick, a steerable wheel alignment angle, the torque on the rotatable steering column, hydraulic pressure in the at least one hydraulic steering cylinder, operator input torque to the rotatable steering column, current or voltage supplied to the motor, or a combination thereof.
 4. The steerable vehicle of claim 1, wherein the controller is configured to output second control signals to the motor to instruct the motor to drive the rotatable steering column to steer the steerable vehicle along a target route in response to engagement of automatic guidance.
 5. The steerable vehicle of claim 4, wherein the controller is configured to disengage the automatic guidance in response to the magnitude of the torque exceeding a threshold torque.
 6. The steerable vehicle of claim 1, wherein the hydraulic steering valve is coupled to the rotatable steering column at a first location, the motor is coupled to the rotatable steering column at a second location, and the first location is different than the second location.
 7. A steerable vehicle, comprising: a steering mechanism having a rotatable steering column; a first sensor configured to output a first sensor signal indicative of a steering angle of at least one ground-engaging member of the steerable vehicle; a first steering servomechanism comprising a hydraulic steering servomechanism, wherein the hydraulic steering servomechanism comprises a hydraulic steering valve coupled to the rotatable steering column and at least one hydraulic steering cylinder fluidly coupled to the hydraulic steering valve by hydraulic lines, and wherein the hydraulic steering valve is configured to control a hydraulic flow in the hydraulic lines based on a rotational angle of the rotatable steering column to drive the at least one hydraulic steering cylinder to adjust the steering angle of the at least one ground-engaging member; a second steering servomechanism comprising an electric power steering servomechanism, wherein the electric power steering servomechanism comprises a motor configured to control a torque on the rotatable steering column to establish a steering assistance characteristic; a controller communicatively coupled to the first sensor and to the motor, wherein the controller is configured to control the steering assistance characteristic by outputting control signals indicative of a magnitude and a direction of the torque based at least in part on the first sensor signal to influence steering of the steerable vehicle; and a human-machine interface (HMI) configured to receive input commands indicative of selection of one of a plurality of programmed modes of operation of the second steering servomechanism; wherein the at least one ground-engaging member is not coupled to the rotatable steering column by a mechanical linkage; wherein a first programmed mode of operation of the plurality of programmed modes of operation comprises steering during movement of the steerable vehicle within a field headland, and a second programmed mode of operation of the plurality of programmed modes of operation comprises steering during movement of the steerable vehicle within a field and along a road; wherein the first programmed mode of operation comprises a steering feedback sub-mode, a torque-free sub-mode, an automatic steering centering sub-mode, and a lock-to-lock assistance sub-mode; and wherein the second programmed mode of operation comprises a steering feedback sub-mode, an automatic steering centering sub-mode, and a torque-free sub-mode.
 8. The steerable vehicle of claim 7, wherein the first sensor comprises a Hall effect sensor.
 9. The steerable vehicle of claim 7, comprising a second sensor configured to output a second sensor signal indicative of the torque applied to the rotatable steering column, wherein the controller is communicatively coupled to the second sensor, and the controller is configured to control the steering assistance characteristic by outputting the control signals indicative of the magnitude and the direction of the torque based at least in part on the first sensor signal and the second sensor signal.
 10. The steerable vehicle of claim 9, wherein the controller is configured to output second control signals to the motor to instruct the motor to drive the rotatable steering column to steer the steerable vehicle along a target route in response to engagement of automatic guidance, and the controller is configured to disengage the automatic guidance in response to receiving the second sensor signal indicative of the magnitude of the torque exceeding a threshold torque.
 11. The steerable vehicle of claim 7, comprising a third sensor configured to output a third sensor signal indicative of a speed of the steerable vehicle or a speed of the at least one ground-engaging member, wherein the controller is communicatively coupled to the third sensor, and the controller is configured to control the steering assistance characteristic by outputting the control signals indicative of the magnitude and the direction of the torque based at least in part on the first sensor signal and the third sensor signal.
 12. The steerable vehicle of claim 7, comprising a joystick communicatively coupled to the controller, wherein the joystick is configured to output a joystick signal indicative of a position of the joystick, and the controller is configured to instruct the motor to drive the rotatable steering column to rotate based at least in part on the joystick signal.
 13. The steerable vehicle of claim 7, wherein the hydraulic steering valve is coupled to the rotatable steering column at a first location, the motor is coupled to the rotatable steering column at a second location, and the first location is different than the second location. 